Thermoforming installation for producing shaped bodies made of plastic film, and method for producing the same

ABSTRACT

The present invention relates to a thermoforming apparatus ( 1 ) for producing shaped bodies ( 114 ) of plastic sheet ( 50 ), such as cups, containers, lids, secondary packagings for foodstuffs or the like, which comprises a forming station with a two-part forming tool ( 20 ). The two-part forming tool ( 20 ) comprises an upper tool table ( 28 ) adapted to be adjustably fixed and having an upper tool ( 30 ) with pre-stretch means ( 92 ) movably mounted therein, and a movable lower tool table ( 32 ) having a lower tool ( 34 ) with cavities ( 112 ). The movable lower tool table ( 32 ) is guided through the intermediary of guide means ( 42 ) and capable of being approached to the upper tool table ( 28 ) and moved away from it. The guide means ( 42 ) in accordance with the invention for the first time include a rotatable guide rail assembly ( 40 ) whereby the lower tool table ( 32 ) may be guided rectilinearly and rotated together with it. Moreover the present invention relates to a method for manufacturing the shaped bodies ( 114 ) of plastic sheet ( 50 ).

The present invention relates to a thermoforming apparatus for producingshaped bodies of plastic sheet, such as cups, containers, lids, foodpackagings or the like, comprising a forming station with a two-partforming tool, in accordance with the preamble of Claim 1, as well as amethod for producing such shaped bodies in accordance with the preambleof Claim 14.

Thermoforming apparatus have in practice become known in differentvariants and embodiments. For manufacturing container-type articles orshaped bodies of thermoplastic material, a two-part forming tool isused. One forming tool half, the so-called upper tool, is attached tothe upper tool table and generally connected, together with the latter,with the frame or stand of the thermoforming apparatus in an adjustablyfixed manner, so that the upper tool may be adjusted to the respectiveshaped body to be produced. The other forming tool half, the so-calledlower tool, is movably guided in the frame or stand of the thermoformingapparatus.

In order to form the shaped bodies, the forming tool halves, i.e., theupper and lower tools, are arranged in a mutually facing, closedposition. Between the upper and lower tools a plastic sheet is arrangedwhich is usually pre-heated and thus has good ductility, and which ismostly supplied intermittently from a supply reel in the form of a sheetweb.

During the deep-drawing step, the plastic sheet is clamped between theupper and lower tools and thus immobilized. Then the plastic sheet ispressed into the cavities of the lower tool by the pre-stretch means ofthe upper tool, while the rim of the shaped body to be producedcontinues to be clampingly retained between the upper and lower tools.By generating a vacuum in the cavities, or by injection of air, thesheet applies itself against the inner walls of the cavities in thelower tool and thereby assumes the desired shape.

After sufficient cooling of the plastic sheet through contact with thetool surface, which may optionally be cooled actively, the shaped bodiesare severed from the plastic sheet. To this end, the lower tool is movedupwards by about the amount of the sheet thickness. Correspondingcutting edges of the two-part forming tool cut the individual shapedbodies from the sheet web. The remaining sheet matrix is, in turn,usually supplied intermittently to a reeling unit.

In order to remove the shaped bodies from the cavities, the lower toolis subsequently moved away from the upper tool while being rotated aboutits longitudinal axis such that the lower tool faces a stacking means,and the shaped bodies may thus be transferred to the stacking means.

Examples for the above discussed thermoforming apparatus as known frompractice are described, e.g., in U.S. Pat. No. 6,135,756 or DE 33 46 628A1.

These known thermoforming apparatus do, however, have the essentialeconomical drawback of only low cycle frequencies in the order, e.g., ofup to 30 cycles per minute being achievable. Higher cycle frequenciesare not possible without damage to the moved components. These low cyclefrequencies are, however, not acceptable any more in view of the costpressure nowadays prevailing.

Another drawback are the drive mechanisms employed in the knownthermoforming apparatus, as well as the guide means for the lower toolsused there.

The thermoforming apparatus described in DE 33 46 628 A1 specificallyoperates with a two-part forming tool, with the upper tool being fixedlyattached to the stand, and the lower tool being movable. For opening andclosing, the lower tool is aligned towards the upper tool and away fromit and at the same time towards a stacking means, and oriented away fromthe latter back to the upper tool in a combined lifting and rotatingmovement. The lifting and rotating movement of the lower tool isproduced by a cam disc/toggle joint drive. Hereby the lower tool is tobe displaced vertically and at the same time rotated about its ownlongitudinal axis.

The combination of a toggle joint mechanism in conjunction with a camdisc drive employed in the thermoforming apparatus known from DE 33 46628 A1 has a very complex configuration. Even the cam disc drivemechanism itself already exhibits the inherent drawback that it is onlycapable of transmitting limited forces. In addition, high cyclefrequencies cannot be achieved with a cam disc drive mechanism. Cam discdrive mechanisms furthermore tend to wear rapidly, so that they have tobe maintenanced frequently, which raises the operating costs of such athermoforming apparatus in an unacceptable degree. Moreover thepresently discussed thermoforming apparatus in accordance with DE 33 46628 A1 and its complex toggle joint mechanism includes another group ofcomponents which inherently also only allows for low cycle frequencies.

One further drawback of this known thermoforming apparatus resides inthe fact that the process of trimming the completed shaped bodies fromthe plastic sheet consumes comparatively much time while being effectedrather in a cutting or even squeezing manner, so that the respectivecutting edges of the two-part forming tool are worn rapidly. This inturn increases the maintenance expenses, which again has a negativeeffect on the operating costs. An increase in the trimming velocity,such as to be able to reach die-cutting velocities, for example,inherently is not possible in the thermoforming apparatus discussed inDE 33 46 628 A1. Limiting elements in this respect are the cam discswhich have to generate the complex overall movement of the lower tooland also its additional lifting movement for trimming out the completedshaped bodies. If it were desired to raise the trimming velocity, thosecam portions of the cam disc controlling the trimming movement wouldhave to be designed to be substantially shorter, i.e., the associatedangular segment of the cam disc would have to be made smaller, whichdoes, however, result in extremely unfavorable conditions in terms ofactuating forces, and thus in an intolerable increased strain tocomponents. Cam discs strained like this would thus constantly have tobe maintenanced or even replaced, which again unacceptably raises theoperating costs. As a result, the cam discs of DE 33 46 628 A1 define anupper limit not only for the achievable cycle frequencies but also forthe trimming velocity.

The thermoforming apparatus in accordance with U.S. Pat. No. 6,135,756specifically also comprises a two-part forming tool. The guide means ishere, as well, combined with the drive means of the lower tool table, orlower tool, and generates a combined lifting and rotating movement ofthe lower tool through the intermediary of a cam disc crank drive. Thethermoforming apparatus in accordance with U.S. Pat. No. 6,135,756includes two cam disc crank drives arranged on respective outer endfaces of the lower tool. The lower tool has at its outer sides threejournals each, which move in the associated grooved cams or guide trackson the stand, respectively. The grooved cams have an extremely complexgeometry and are adapted such that during opening of the forming tool,the lower tool may be moved downwardly away from the upper tool androtated in order to be able to orient it towards a stacking means andagain rotate it away from the latter. Inasmuch as the complex geometryof the grooved cams and guide tracks is not suited for transmitting theforces necessary for trimming the finished shaped bodies from theplastic sheet, additional cam discs are provided for transmitting therespective necessary forces.

In comparison with DE 33 46 628 A1, this allows to achieve slightlyhigher trimming velocities. The required high trimming velocities fordie-cutting the shaped bodies from the plastic sheet can, however, notbe achieved. The trimming step as before takes place by cutting orsqueezing.

On the other hand, the cam discs of U.S. Pat. No. 6,135,756 aresubjected to substantially higher loads in comparison with DE 33 46 628A1. Accordingly this results in premature wear of these components. Thisnecessitates considerable maintenance work and has a negative effect onoperating costs. Owing to the unfavorable conditions in terms oftransmitting forces, there is still a possibility of the cam discsbreaking before their time and then having to be replaced. This resultsin a standstill of the thermoforming apparatus, with production comingto a complete halt.

Apart from this, the high cycle frequencies nowadays demanded areimpossible with the geometrically complex guide tracks that may only beadapted to each other with great difficulty. Moreover it is not possibleto transmit sufficiently high forces by such guide tracks because theguide pins must serve for transmitting not only the forces for liftingand lowering the lower tool, but also the forces for accelerating,decelerating and tilting or rotating them. Large-sized tools having anumber of cavities that meets present-day demands cannot be realizedwith the teaching of U.S. Pat. No. 6,135,756, for with an increasingsize the weight of the lower tool also increases, so that the forcesthen necessary for the above mentioned movements cannot be transmittedany more.

Furthermore the complex geometry of the plurality of guide tracksnecessitates their constant maintenance, for owing to the high forces,these may easily be damaged, worn out, or lose the demanded runningaccuracy.

Moreover these complex guide tracks present the additional drawback thatcorrect matching of the lower tool during the closing movement towardsthe upper tool cannot be ensured. Correctly matching the lower tool withthe upper tool is, however, an essential precondition for the repeatablemanufacture of dimensionally accurate shaped bodies, particularly athigh cycle frequencies, in order to avoid undesirable scrap.

In view of the above, it is an object of the present invention toimprove known thermoforming apparatus in such a way that substantiallyhigher cycle frequencies may be achieved, and an economical operation ofthermoforming apparatus thus improved becomes possible. Moreover it isan object of the present invention to propose an economical method forproducing shaped bodies of plastic sheet.

What is proposed in accordance with the invention is a thermoformingapparatus for producing shaped bodies of plastic sheet, such as cups,containers, lids, food packagings or the like, comprising a formingstation with a two-part forming tool. The two-part forming toolcomprises an upper tool table adapted to be adjustably fixed and havingan upper tool with pre-stretch means movably mounted therein, and amovable lower tool table having a lower tool with cavities. The movablelower tool table is guided through the intermediary of guide means andcapable of being approached to the upper tool table and moved away fromit by drive means.

Here it is provided for the first time that the guide means include arotatable guide rail assembly whereby the lower tool table may be guidedlinearly, or rectilinearly, and rotated together with it. Thus the lowertool table may advantageously perform a clearly defined rectilinearlifting movement without at the same time having to perform a rotatingmovement about its own longitudinal axis in the disadvantageous mannerknown from the prior art.

The rotating movement of the lower tool for ejecting the completedshaped bodies is, in accordance with the invention, advantageouslyachieved through the capability of rotating the guide rail assemblywithout the lower tool table having to be rotated relative to itself,e.g., about its longitudinal axis. This advantageously ensures that thelower tool may be supplied correctly to the upper tool in each liftingmovement towards the latter, and thus repeatably matched in an accurateposition, so that the lower tool will always contact the upper tool inthe same way.

Rotatability of the guide rail assembly in combination with uncouplingthe rotating movement from the linear lifting movement furthermoreprovides the advantage that the repeating accuracy of the axial orrectilinear lifting movement of the lower tool is neither falsifyinglysuperseded nor impaired in any other negative manner by the rotatingmovement. Moreover, when the lower tool is in the lowered condition, orin the condition removed from the upper tool, it may be rotated out ofthe frame of the thermoforming apparatus and accurately aligned with astacking means through the intermediary of the rotatable guide railassembly. Advantageously the lower tool with the finished shaped bodieslocated therein may thus optimally be aligned in this position relativeto the stacking means, matched with the latter, and optionally movedtowards and/or away from it, again in an advantageous linear movement.

Furthermore the novel guide means with a rotatable guide rail assemblyprovide the additional advantage that the lower tool with known andcorrespondingly perfected coupling members may be mounted in an axiallymovable manner or guided rectilinearly between the guide rails of therotatable rail assembly, so that the only forces that must be absorbedby the coupling members are guiding forces, and the actualmovement-generating forces for the lifting movement towards the uppertool and away from it, as well as for a die-cutting movement, may betransmitted to the lower tool table via a drive mechanism actingdirectly on the lower tool table, so that the guiding mechanism of thelower tool table advantageously is no more subjected to these highforces. In this way, any desirable high forces may be transmitteddirectly to the lower tool table without the risk as known from theprior art, such as inevitable wear or even breakage of the prior-artcombinations of cam discs and guide pins running in guide rails that aresubjected to the entire drive force.

In a preferred embodiment of the thermoforming apparatus in accordancewith the invention, the rotatable guide rail assembly of the guide meansfor the first time includes two rotatable guide rails linked to a frameof the thermoforming apparatus, wherebetween the lower tool table isguided so as to be capable of being linearly, or rectilinearly,approached towards the upper tool table and moved away from it. Inaccordance with a further preferred embodiment of the thermoformingapparatus in accordance with the invention, the drive means for thelower tool table have the form of a crankshaft drive mechanism.

Hereby symmetrical guidance of the lower tool table is achieved. Thisadvantageously results in a particularly accurate lifting movement ofthe lower tool table. As the lower tool table is guided on both sides,it may not only be aligned and guided correctly in parallel with theupper tool table, but moreover this advantageously brings about theadditional synergy effect of centrally driving the tool table up anddown, or towards the upper tool and away from it, from below in itscenter through the intermediary of the drive means having the form of acrankshaft drive mechanism. Moreover the crankshaft drive mechanism mayadvantageously also attack in several locations at the lower tool tablevia suitable coupling means, so that maximum possible forces may betransmitted to the lower tool table at minimum flexure or deformationthereof.

The crankshaft drive mechanism provides the major advantage of a cyclefrequency theoretically having no upper limitations. With the crankshaftdrive mechanism it is for the first time possible to readily realizecycle frequencies of 40 cycles, 50 cycles, or substantially more cycles.Here the linear or rectilinear movement of the lower tool table issynergistically utilized in combination with the crankshaft drivemechanism so as to attain such high cycle numbers for the first time.

This motion principle is known from the reciprocating internalcombustion engine where, however, the pressing force generated by theexplosion of the compressed fuel mixture is inversely transmitted by therectilinear up-and-down movement of the reciprocating piston to aconnecting rod and from the latter to a crank shaft, to achieve a rotarymovement of the drive train and thus of the vehicle's wheels. In thepresent invention, an externally impressed rotary movement is for thefirst time converted via the crankshaft drive mechanism into a linearlifting movement, so as to be capable for the first time to drive thelower tool of a thermoforming apparatus on the one hand withsufficiently high forces and on the other hand sufficiently rapidly, soas to achieve cycle frequencies of 40 cycles, 50 cycles, or more. Suchhigh cycle frequencies had hitherto been thought unattainable.

Moreover the inventive combination of a crankshaft drive mechanismcombined with a linear or rectilinear guidance of the lower tool tableprovides the additional advantage of extremely low wear in comparisonwith the known thermoforming apparatus, so that the operating costs ofthe thermoforming apparatus in accordance with the invention may belowered decisively, and down times may moreover be avoided. Thus it isnot only possible to clearly raise the output of a thermoformingapparatus in accordance with the invention, but at the same time toattain an altogether positive cost-efficiency ratio by reducing theoperating expenses thanks to a particularly reliable design.

In accordance with a further preferred embodiment of the thermoformingapparatus in accordance with the invention, the crankshaft drivemechanism is positioned inside the frame of the thermoforming apparatusat the side of the lower tool table facing away from the upper tooltable, such that the center point of the crank shaft axis, the centerpoint of the eccentric axis portion thereof in the upper reversingpoint, the linking points of the rotatable guide rails, and the linkingpoints at the lower tool table come to lie on an imaginary common linewhen the lower tool table reaches its upper reversing point. Thus it isadvantageously ensured that in the upper reversing point of the lowertool, and thus in the closed condition of the forming tool, a maximumforce is ensured by the drive mechanism owing to the linear force fluxacross all of the participating coupling members from the crankshaftdrive mechanism to the lower tool table, so that losses of force can notoccur or unfavorable conditions in terms of attacking forces can notmanifest. This is particularly advantageous if in this position anadditional impulse of a die-cutting stroke for producing a die-cuttingmovement is to be transmitted via these components.

In another preferred embodiment of the thermoforming apparatus inaccordance with the invention, the eccentric shaft portion of thecrankshaft drive mechanism is linked, preferably centrally, in the lowertool table through the intermediary of a connecting rod. This providesthe advantage of direct force transmission from the crankshaft drivemechanism to the lower tool table. The multi-part toggle jointmechanisms known from the prior art may thus be avoided. Moreover thisprovides the advantage that a number of load-bearing components as smallas possible may be calculated and optionally optimized with a view tooptimum introduction and transmission of force, e.g., with the aid offinite-element methods. Thus it is also possible, as early as in thepreparatory stage, to keep the development costs low.

In a further preferred variant of the thermoforming apparatus inaccordance with the invention, the connecting rod has towards the lowertool table a Y-shaped cross-section so as to branch out into two armsand act on the lower tool table via two spaced-apart locations. Thisadvantageously allows an optimum impression of the forces for moving thelower tool table without having to fear any inadmissible deformation orflexure of the lower tool table. By skillfully selecting the linkingpoints it is possible to optimize the force flux in the lower tool tablesuch that the latter will not suffer any flexure or deformation evenwhen a maximum force is impressed for performing a die-cutting stroke.

In accordance with another preferred embodiment of the thermoformingapparatus of the invention, the crankshaft drive mechanism includes anelectric servomotor. This provides the advantage of, e.g., programmablecontrol or automatic control, so that the respective rotationalcharacteristics of the servomotor may be adapted optimally to therespective application. Such optimization of the movement sequences isnot possible with the cam disc drive mechanisms that are known from theprior art to constitute a drawback.

In a further preferred embodiment of the thermoforming apparatus it ismoreover provided that the electric servomotor drives the crankshaftdrive mechanism through the intermediary of a toothed belt via a pulley.This provides cost-efficient drive technology with well-triedcomponents. In addition, gears, worm drives or the like are equallyconceivable for force transmission from the servomotor to the crankshaftdrive mechanism. Moreover the servomotor may act directly on the crankshaft. This provides the advantage of a highly compact design.

In a further preferred embodiment of a thermoforming apparatus inaccordance with the invention, it is proposed for the first time thatthe lower tool table, when in a position removed from the upper tool, iscapable of being rotated out of the frame of the thermoforming apparatusand associated with a stacking means, so that the lower tool table thenfaces the opposed stacking means, and optionally may also be approachedtowards and moved away from the latter.

This results not only in the advantages already discussed above, but inaddition the lower tool may be aligned with the stacking means andapproached towards it in such a way that the completed shaped bodieslocated in the lower tool may be transferred optimally, without anyjamming and with the necessary repeating accuracy, to the stacking meanswhich is then located in exact opposition. Rotatability of the railassembly thus ensures that the lower tool is positioned in exactopposition with the stacking means and may accurately be aligned withit. The capability of linear or rectilinear movement of the lower tooltable inside the rotatable rail assembly moreover provides thesynergetic advantage that the lower tool may, e.g. through theintermediary of the crankshaft drive mechanism, be approached towardsthe stacking means and again moved away from the latter in a lifting orup-and-down movement so that, e.g. in the event of shaped bodies havingdifferent sizes, it is possible to additionally compensate for thedistance to be covered by the shaped bodies out of the cavity of thelower tool and across to the stacking means. Particularly in combinationwith ejectors present in the lower tool, an optimum adaptation of thetransfer movement of the shaped bodies out of the cavities of the lowertool into the associated reception points of the stacking means may thusbe ensured.

It is another advantage that differently designed stacking means may inthis way be utilized together with the thermoforming apparatus inaccordance with the invention, so that it is possible to employ stackingmeans which are furthermore optimized with regard to the respectiveshaped bodies to be manufactured without any additional expenditure foradaptation.

In accordance with a further preferred embodiment of the thermoformingapparatus in accordance with the invention, ejector drive means forlifting and lowering ejectors movably arranged in the lower tool arearranged at the lower tool table, preferably between the two arms of theY-shaped connecting rod which face the lower tool table. This provideson the one hand the advantage that ejection of the completed shapedbodies with the aid of the ejectors may be supported, and the shapedbodies may be furnished with an additional impulse of motion, so thatthey may readily cover the distance from the lower tool to the stackingmeans. On the other hand, arranging the ejector drive means underneaththe lower tool table provides the additional advantage that the freeconstruction space remaining there, for instance between the arms of theY-shaped connecting rod, may be used optimally and thus a design of thethermoforming apparatus in accordance with the invention may be achievedwhich is as compact as possible.

In a further preferred variant of a thermoforming apparatus inaccordance with the invention, it is proposed for the first time thatsecond drive means are provided for lifting the lower tool tabletogether with its drive means within the guide means linearly orrectilinearly guiding it, in a predetermined stroke for generating adie-cutting movement.

Thus, e.g. in combination with the crankshaft drive mechanism not only ahigh cycle frequency as such is ensured, but at the same time a highcycle frequency of the die-cutting stroke generating the die-cuttingmovement is moreover possible. Die-cutting strokes may thusadvantageously be performed in less than 1/10 of a second. By liftingthe lower tool table within its rectilinear guidance for generating thedie-cutting movement, it is advantageously ensured that the lower toolwill always matingly co-operate with the upper tool, so that jamming orthe like is precluded even during die-cutting, and thus an undesirablewear of the cutting edges is avoided. Moreover it is ensured that inthis manner the substantially higher forces for a die-cutting stroke incomparison with the cutting or squeezing movements known from the priorart may readily be transmitted to the lower tool table in asubstantially shorter time. Furthermore it is ensured that these forcesmay be transmitted to the lower tool table not only rapidly, i.e.,during a short period of time, but also with a high repeating frequency,so that altogether a high cycle frequency of the thermoforming apparatusin accordance with the invention may be attained as regards both theshaping cycles for closing and opening the forming tool, and also thedie-cutting cycles for trimming out the shaped bodies in the closedcondition of the forming tool.

In correspondence with another preferred embodiment of the thermoformingapparatus in accordance with the invention, the second drive means forgenerating the die-cutting stroke include a hydraulically driven liftingcylinder. This provides the advantage that in comparison withconventional cam disc drive mechanisms and also in comparison with theadvantageous crank drive mechanism of the thermoforming apparatus inaccordance with the invention for driving the lower tool table, it ispossible to impress even far higher forces to the lower tool table insubstantially shorter force development times, so that an optimumdie-cutting impulse may be achieved through the selection of a hydraulicdie-cutting drive mechanism. Furthermore a hydraulic drive mechanismpermits optimum regulation similar to the crankshaft drive mechanismdriven through the intermediary of an electric servomotor, accordinglyallows for automatic process management, and thus may be harmonizedoptimally with the crankshaft drive mechanism. Hereby it isadvantageously ensured that the die-cutting stroke will always beimpressed precisely when the lower tool is in the upper reversing pointand the forming tool accordingly is in the closed condition.

In accordance with a further preferred embodiment, the stroke of thesecond drive means is about 3 mm to 10 mm, preferably 5 mm to 8 mm, in aparticularly preferred manner 1.1 to 1.3 times the thickness of aplastic sheet. This ensures optimum die-cutting results upon trimmingthe completed shaped bodies from the plastic sheet clamped between theupper and lower tools. At the same time, particularly clean rims anddie-cut edges are thus achieved at the rims of the die-cut shapedbodies, so that the rims of the shaped bodies need not be subjected toan additional finishing step such as for application of a lid or thelike.

A method for producing shaped bodies of plastic sheet, such as cups,containers, lids, secondary packagings for foodstuffs or the like withthe aid of a thermoforming apparatus of the general type as known in theprior art is being proposed, which method comprises the following steps:a) closing the forming tool by guiding the movable lower tool tablethrough the intermediary of the guide means and driving it through theintermediary of the drive means such that it is approached towards theupper tool table, b) producing the shaped bodies in the closed conditionof the forming tool, c) opening the forming tool by guiding the movablelower tool table through the intermediary of the guide means and drivingit through the intermediary of the drive means such that it is movedaway from the upper tool table, and d) ejecting the shaped bodies,optionally into a stacking means. In accordance with the invention it ishere proposed for the first time that the lower tool table is guidedrectilinearly through the intermediary of a rotatable guide railassembly for closing and opening the forming tool, and rotated togetherwith it for ejecting the shaped bodies. This serves to achieve theadvantages and synergy effects already discussed above.

In a preferred development of the method in accordance with theinvention, the lower tool table is driven through the intermediary ofdrive means having the form of a crankshaft drive mechanism. Theadvantages and synergy effects thus attainable have already beendiscussed above. In accordance with another preferred development of themethod in accordance with the invention, the lower tool table, when in aposition removed from the upper tool table, is rotated with therotatable rail assembly out of the frame of the thermoforming apparatusand associated to a stacking means, so that the lower tool table facesthe stacking means then having an opposed position, and optionally mayalso be approached towards and moved away from the latter. Moreover inaccordance with a further preferred embodiment of the method inaccordance with the invention, the lower tool table with its drive meansis raised and again lowered within the guide means rectilinearly guidingit through the intermediary of second drive means, for generating adie-cutting movement with a predetermined die-cutting stroke. Theadvantages and synergy effects in this regard have also already beendiscussed above.

The invention shall in the following be explained in more detail by wayof embodiments while referring to the figures of the drawing, wherein:

FIG. 1 is a front view of an embodiment of a thermoforming apparatus inaccordance with the invention;

FIG. 2 is a side view of the exemplary embodiment of a thermoformingapparatus in accordance with the invention as represented in FIG. 1;

FIG. 3 is a laterally viewed detail of the drive mechanism for rotatingthe guide rail assembly of the variant of a thermoforming apparatus inaccordance with the invention as shown in FIGS. 1 and 2;

FIG. 4 is a sectional view along line X-X of FIG. 3;

FIG. 5 represents the variant shown in FIGS. 1 through 4 in an obliquelypositioned operational arrangement;

FIG. 6 is a three-dimensional, schematically simplified view of themovable component groups of an exemplary embodiment of a thermoformingapparatus in accordance with the invention, with arrows symbolizing thelinear lifting movement of the lower tool table;

FIG. 7 is a three-dimensional, schematically simplified view of thevariant shown in FIG. 6, with different arrows symbolizing thedie-cutting movement of the lower tool table; and

FIG. 8 is a three-dimensional, schematically simplified view of thevariant shown in FIGS. 6 and 7, again with different arrows symbolizingthe movement upon rotation of the guide rail assembly.

FIG. 1 represents an exemplary embodiment of a thermoforming apparatus 1in accordance with the invention in a front view. The movable componentgroups of the thermoforming apparatus 1 are arranged in a stand 2. Thestand 2 may, for instance, be constructed in the form of stand panels ofsheet steel which are stress-relieved by annealing. A cross-member 4arranged underneath, i.e., near the ground, connects the stand panels 2and at the same time serves as a bed for the bearings of the crankshaftdrive mechanism 6. The crankshaft drive mechanism 6 is in the presentlyrepresented variant driven by an electric servomotor 8. The drive forceof the latter is transmitted via a belt 10 and pulleys 12 and 14, whichis more clearly visible particularly in the side view of FIG. 2. In thepresently represented variant, the crankshaft drive mechanism 6 ismounted symmetrically on both sides in relatively short lever arms 16,with the lever arms 16 in turn being linked to a bracket 18 mounted onthe cross-member 4.

Both in FIG. 1 and in FIG. 2, the two-part forming tool 20 of theforming station of the thermoforming apparatus 1 is represented in theclosed condition approximately in the center of the drawing. Across-member 24 visible in the upper section of FIG. 1 and FIG. 2connects the two stand panels 2 above the two-part forming tool 20 andserves as a base for a drive mechanism 26 for adjusting the position ofthe upper tool table 28 with the upper tool 30 attached thereto. Thedrive mechanism 26 for adjusting the position of the upper tool table 28may, e.g., have the form of a precision lifting mechanism with backlashcompensation. A lower tool table 32 supports the lower tool 34 and isarranged between the rotatable guide rails 38 of the rotatable guiderail assembly 40 (cf. FIGS. 3 and 4) of the guide means 42 through theintermediary of correspondingly designed linear guides 36. At theunderside or bottom of the lower tool table 32, ejector cylinders 44 andthe upper connecting rod bearings 46 are attached.

Between the upper tool 30 and the lower tool 34 of the forming tool 20represented in the closed condition in FIGS. 1 and 2, a chain transportmeans 48 is shown whereby the plastic sheet 50 is supplied to thetwo-part forming tool 20 and transported off following forming andtrimming out of the shaped bodies that are not shown here any more, withthe plastic sheet 50 being tensioned by correspondingly suitable meansin the range of the two-part forming tool 20, preferablybidirectionally.

The upper tool table 28 is guided in correspondingly designed linearguides 52 between the stand panels 2. The lower tool 34 may, e.g., havea mounting surface of 490 mm×1040 mm. Thus, e.g., four rows of eightcavities each for 32 shaped bodies may be realized at a diameter of theshaped bodies of about 75 mm. This amounts to a total die-cutting lengthof all edges to be severed of 7640 mm, necessitating a total die-cuttingforce of about 400 kN.

The upper tool 30 is fastened to the upper tool table 28, for examplewith the aid of spacers (not shown). Guide rails (not shown) facilitatemounting of the tools. A backlash compensation 54 serves forcompensating play, e.g., during precision lifting 26 of the upper tooltable 28. The linear guides 36 for the lower tool table 32 have aplay-free adjustment and ensure accurate guiding of the lower tool 34.The linear guides 52 of the upper tool table 28 include slideways (notshown) which may be adjusted without play.

The ejector drive means 44, positioned underneath the lower tool table32, for the ejectors 56 visible in FIG. 2 in a fragmentary sectionalview, include two pneumatic cylinders with stroke-arresting means.

The connecting rod 58 driven by the crankshaft drive mechanism 6, whichmay also be referred to as a driving rod for driving the lifting strokeof the lower tool table 32, has the form of a triangle or of a Y in thepresently represented variant. The connecting rod 58 is linked to theeccentric shaft portion 62 of the crankshaft drive mechanism 6 through afirst connecting rod portion 60. The two upwardly directed arms 64 ofthe Y-shaped connecting rod 58 in the views of FIGS. 1 and 2 are linkedto the connecting rod bearings 46 of the lower tool table 32. These twoupper connecting rod bearings 46 here have an arrangement, if possible,where a flexure of the lower tool table 32 as well as its proper weightmay be kept as low as possible. The Y-shaped connecting rod 58advantageously has only one bearing at the lower connecting rod portion60 of the presently represented variant, so that even one crank drivemechanism is sufficient.

As was already explained in the foregoing, the crankshaft drivemechanism 6 is mounted in two locations so as to better resist flexure.The respective crank bearings may be split for the purpose of easiermounting. The crankshaft drive mechanism 6 is centrally mounted in leverarms 16 forming a kind of double rocker. The latter in turn is mountedon the cross-member 4 by its right side through the intermediary of thebracket 18. On the left side of this double rocker, the die-cuttingdrive mechanism 64 attacks. The die-cutting drive mechanism 64 consists,e.g., of a hydraulic cylinder and an associated hydraulic system forgenerating with the aid of the hydraulic cylinder an abrupt cuttingstroke that is transmitted via the double rocker 16, the crankshaftdrive mechanism 6, the connecting rod 58, and the bearings 46 to thelower tool table 32 and thus to the lower tool 34.

The drive mechanism of the crankshaft drive mechanism 6 may—as wasalready mentioned above—include as the lifting drive mechanism aservomotor 8 which acts on the crankshaft drive mechanism 6 viatransmission, toothed belt, ladder chain drive, or the like with littleplay. Closing and opening of the two-part forming tool 20 thencorrespond to respective 180-degree rotations at the crank shaft.

The pivoted levers 38 for rotatably accommodating the lower tool table32, which were already represented in FIGS. 1 and 2, include in thepresently represented variant, e.g., the pivoted lever lateral guides 66having the form of cam rollers as represented in FIG. 3. The lateralguide members 66 of the pivoted levers 38 having, e.g., the form of camrollers, run on hardened rails (not shown) and may be adjusted free fromplay for accurately guiding the lower tool 34.

As a drive mechanism for rotating the rotatable guide rails 38 of therotatable guide rail assembly 40, one driving rod 68 each is provided oneither side of the lower tool table 32. As a drive mechanism 70 forgenerating the rotating movement of the lower tool 34 via the rotatableguide rails 38, it is possible to provide a driving rod pivotal drivemechanism 68 acting on both guide rails 38 which may be driven, e.g., bya geared servomotor 72 and a synchronized shaft 74. These details arerepresented more closely in FIG. 4 which shows a sectional view alongline X-X of FIG. 3.

In order to limit the rotating movement into the frame, or into thestand 2, a pivoted lever stop 76 in accordance with the representationof FIG. 3 is provided. This stop 76 for the pivoted lever 38 may beadjusted for accurately positioning the lower tool 32.

The drive mechanism 84 for adjusting the upper tool table 28, which may,e.g., have the form of a precision drive, serves not only for adjustingthe die-cutting stroke, for example, but may also be employed foractivation or deactivation of the die-cutting stroke. Two threadedspindles 78 barely visible in FIGS. 1 and 2 are driven, e.g., throughworm gears 80 via a synchronized shaft 82 through the intermediary of ageared motor 84.

In the presently represented variant in accordance with FIGS. 1 to 5,two backlash compensations 54 exemplarily having the form of pneumaticbellows cylinders are capable of drawing the upper tool table 28upwardly through the intermediary of drawbars (not shown) so as tocompensate for backlash between spindle and nut.

As is represented more closely in FIG. 2, a pre-stretch unit 86 isprovided. The presently represented variant of the pre-stretch unit 86includes, i.a., a pre-stretch means drive mechanism 88 having the formof a servomotor, which is coupled to the pre-stretch means plate 90 andthe pre-stretch means 92 arranged thereon via a toothed belt drive notshown in FIG. 2 and a planetary roller threaded drive and the nutthereof through releasable connections. This pre-stretch means drivemechanism may also include a highly dynamic servomotor 88.

In the variant of the pre-stretch means drive mechanism of thepre-stretch unit 86 shown more closely in FIG. 1, the latter may includea console 94 supporting a hydraulic cylinder 96 as the pre-stretch meansdrive mechanism. The hydraulic cylinder 96 is linearly displaced withthe console 94 together with the upper tool table 28 while stationaryrelative to the latter. The distance between the hydraulic cylinder 96and the upper tool table 28 thus remains permanently constant. Thehydraulic cylinder 96 is encapsulated by a housing 98, so that hydraulicoil cannot spill even in the event of minor leakages. A thrust bar 100is linked to the hydraulic cylinder 96 in accordance with therepresentation in FIG. 1, and in the presently represented variant itsone end facing away from the hydraulic cylinder 96 is linked to theright end of a rocking lever 102. The rocking lever 102 is pivotedthrough the intermediary of a bearing mount 104. The bearing mount 104in turn attacks at the upper tool table 28 via a suitable bracket. Atthe left end of the rocking lever 102, the pre-stretch means rod 106 islinked which is connected with the pre-stretch means plate 90 and thepre-stretch means 92 attached to the latter. The hydraulic cylinder 96for driving the pre-stretch means 92 may include a servo controlcontaining a programmable control for the stroke of the cylinder 96. Thenecessary hydraulic unit may be positioned inside the bottom part of themachine. The pre-stretch means rod 106 may be connected with thepre-stretch means plate 90 in the upper tool 30 via a compensatingcoupling. The housing 98 for the hydraulic cylinder 96 not only servesfor entrapping any leakages, but may also support the servo control andmoreover contain sensors or the like in order to report any occurringleakages, and may be provided with means for discharging such leakages.The same also applies to the hydraulic conduits.

In accordance with the representation of FIG. 2, the thermoformingapparatus 1 of the invention may be associated with a stacking means 108for receiving, stacking and transporting the completed shaped bodiesfollowing ejection from the cavities of the lower tool 34. For thispurpose, the stacking means 108 may include, e.g., a catcher 110 fortransporting off the ejected shaped bodies.

The exemplary embodiment of a thermoforming apparatus 1 in accordancewith the invention and represented in FIGS. 1 to 5 is shown in FIGS. 6to 8 in a schematically simplified manner in three-dimensional views forvisualizing the moving sequences while being reduced to the essentialmoved components. For convenience, identical components or componentshaving an identical or similar action will be provided with the samereference symbols as discussed above.

In FIG. 6 the generation of the lifting movement of the lower tool 32 isrepresented in a schematically simplified manner. In the positionrepresented there, the lower tool 32 is removed from the upper tool 30.Three rows of eight cavities 112 each with the completed shaped bodies114 contained in them are visible. The arrow 116 symbolizes the linearmovement of the lower tool 34, or lower tool table 32, which is heredirected downwards. The tool table 32 is linearly guided between therotatable guide rails 38. The arrow 118 symbolizes the servo-electricdrive mechanism for the rectilinear movement of the lower tool 34relative to the rotatable guide rail 38.

The die-cutting cylinder 64 is connected with the two lever arms 16forming a double rocker via a thrust/draw rod 120 and a thrust/drawshaft 122, in order to transmit a cutting stroke—indicated by arrows 124and 126 in FIG. 7—to the lower tool 34. Hereby the completed shapedbodies 114 may be die-cut from the plastic sheet 50 (not shown). In theschematically simplified variant represented in FIG. 7, the hydraulicdrive mechanism for die-cutting is operated while the eccentric shaftportion 62 of the crankshaft drive mechanism 6 and the rotational drivemechanism 70 are stationary.

The crankshaft drive mechanism 6 transmits the moving force for liftingand lowering the lower tool table 32, or for opening and closing theforming tool 20, to the lower tool table 32 through the intermediary ofa connecting rod 58 having a Y shape in this representation. The twoupper arms 64 of the connecting rod 58 have a small support width.

As discussed above, FIG. 7 represents in a schematically simplifiedmanner the generation of the cutting stroke. Accordingly, FIG. 8 showsin a schematically simplified manner the generation of the rotatingmovement.

Here a servo-electric drive mechanism 70 serves for generating therotating movement of the rotatable guide rail 38 with the lower tool 34rectilinearly or linearly guided in it. This is symbolized by the arrows128 and 130.

The present invention for the first time advantageously proposes athermoforming apparatus for producing shaped bodies of plastic sheet,such as cups, containers, lids, secondary packagings for foodstuffs orthe like, comprising a forming station with a two-part forming tool. Thetwo-part forming tool comprises an upper tool table adapted to beadjustably fixed and having an upper tool with pre-stretch means movablymounted therein, and a movable lower tool table having a lower tool withcavities. The movable lower tool table is guided through theintermediary of guide means and capable of being approached to the uppertool table and moved away from it by drive means. In accordance with theinvention, the guide means for the first time include a rotatable guiderail assembly whereby the lower tool table may be guided rectilinearlyand rotated together with it. Furthermore the present invention relatesto a method for producing the shaped bodies of plastic sheet.

Besides the advantages and aspects of the thermoforming apparatus inaccordance with the invention that were already discussed in theforegoing, it provides the following additional advantages:

The lower tool and the lower tool table do not perform a rotatingmovement but only a linear movement when the forming tool is opened andclosed. This ensures more accurate guiding of the tool table incomparison with the prior art. In addition, masses may be managedsubstantially better in a linear movement than in a rotation which maygenerate rotary oscillations that can only be managed with difficulty.In the disadvantageous cam discs known from the prior art, such changinginertial forces necessitated additional complementary cam discs, whichbrought about an additional increased complexity of construction. Thecrank drive mechanism proposed for the thermoforming apparatus inaccordance with the invention, on the other hand, may absorb inertiaforces in both directions which thus already may be managed more easily.In addition, through the intermediary of the crankshaft drive mechanisma fast sinusoidal velocity profile is generated. This provides thefurther advantage that there are no abrupt accelerations ordecelerations of the lower tool. As the connecting or driving rod has atriangular or Y shape and attacks underneath the lower tool, thisadvantageously results not only in a small flexure of the lower tooltable approaching zero, but moreover advantageously even a singlecrankshaft drive mechanism is sufficient. This advantageously helpsreduce the number of components and thus reduce costs. For ejecting theshaped bodies, the lower tool is rotated at a large radius through theintermediary of the rotatable guide rail assembly. Not only does thisprovide the advantages already discussed in the foregoing, but theso-called catcher plate may be omitted that is frequently felt to be adrawback in the prior art. Moreover the stacking means or its stackingbasket, respectively, may be designed to be stationary. This in turnadvantageously results in a simplified construction. Furthermore theseparate hydraulic die-cutting drive mechanism, in contrast with thedisadvantageous cam discs with die-cutting cams as known from the priorart, generates a an abrupt cutting movement, as it were. Thisadvantageously results in prolonged service life times of the tools. Itis another advantage that with the abrupt die-cutting movement,die-cutting times may not only be less than 1/10 s but even less than 30ms.

With the thermoforming apparatus in accordance with the invention it ispossible to process plastic sheets of PP, PS, PE, PET, ABS or PVC. Theplastic sheet supplied to the thermoforming apparatus as a sheet web mayhave a sheet web width of at least 250 mm to 750 mm, at a sheet webthickness of at least 0.3 mm to 4 mm. The available forming area betweenthe upper and lower tools is at least 700 mm×450 mm. The maximumclamping force is at least 400 kN at a maximum cutting length of atleast 8400 mm.

LIST OF REFERENCE SYMBOLS

-   1 thermoforming apparatus-   2 mount or frame-   4 lower cross-member-   6 crankshaft drive mechanism-   8 electric servomotor-   10 belt-   12 pulley-   14 pulley-   16 lever arm-   18 bracket-   20 two-part forming tool-   22-   24 upper cross-member-   26 upper tool drive mechanism adjustment-   28 upper tool table-   30 upper tool-   32 lower tool table-   34 lower tool-   36 lower tool table linear guide means-   38 rotatable guide rails-   40 guide rail assembly-   42 guide means-   44 ejector drive means-   46 connecting rod bearing-   48 chain transport means-   50 plastic sheet-   52 upper tool table linear guide means-   54 backlash compensation-   56 ejector-   58 connecting rod-   60 first connecting rod portion-   62 eccentric shaft portion-   64 die-cutting drive mechanism-   66 pivoted lever lateral guides-   68 driving rod pivotal drive mechanism-   70 rotational drive mechanism-   72 geared servomotor-   74 synchronized shaft-   76 pivoted lever stop-   78 threaded spindle-   80 worm gear-   82 synchronized shaft-   84 geared motor-   86 pre-stretch unit-   88 pre-stretch means drive mechanism-   90 pre-stretch means plate-   92 pre-stretch means-   94 console for pre-stretch means drive mechanism-   96 hydraulic pre-stretch cylinder-   98 housing-   100 thrust bar-   102 rocking lever-   104 rocking lever bearing mount-   106 pre-stretch means rod-   108 stacking means-   110 catcher-   112 cavities-   114 shaped bodies-   116 arrow symbolizes linear movement-   118 arrow symbolizes rotating crank drive mechanism-   120 thrust/draw rod-   122 thrust/draw shaft-   124 arrow symbolizes die-cutting stroke-   126 arrow symbolizes die-cutting movement-   128 arrow symbolizes rotary drive-   130 arrow symbolizes rotation

1. A thermoforming apparatus for producing shaped bodies of plasticsheet, such as cups, containers, lids, secondary packaging forfoodstuffs or the like, comprising a forming station with a two-partforming tool, wherein the two-part forming tool comprises an upper tooltable adapted to be adjustably fixed and having an upper tool withpre-stretch means movably mounted therein, and a movable lower tooltable having a lower tool with cavities, wherein said movable lower tooltable is guided through the intermediary of guide means and capable ofbeing approached to said upper tool table and moved away from it byfirst drive means, wherein said guide means include a rotatable guiderail assembly whereby said lower tool table may be guided rectilinearlyand rotated together with said guide rail assembly, and wherein therotatable guide rail assembly includes two guide rails, pivot-mounted ona frame of the thermoforming apparatus, with the lower tool table beingguided movably between those, in a rectilinear manner, to be approachedtowards the upper tool table and moved away from the latter,characterized in that said first drive means for said lower tool tablehave the form of a crankshaft drive mechanism, said eccentric shaftportion of said crankshaft drive mechanism is linked, preferablycentrally, to said lower table through the intermediary of a connectingrod, said crankshaft drive mechanism are positioned inside said frame ofsaid thermoforming apparatus at a side of said lower tool table facingaway from said upper tool table such that the center point of thecrankshaft axis, the center point of the eccentric axis portion thereofin the upper reversing point, the linking points of said rotatable guiderails, and the linking points at said lower tool table come to lie on animaginary common straight line when the latter reaches its upperreversing point, said lower tool table is capable of being lifted bysecond drive means together with its first drive means within said guidemeans rectilinearly guiding it in a predetermined stroke for generatinga die-cutting movement, and ejector drive means for lifting and loweringejectors movably arranged in said lower tool are arranged at said lowertool table.
 2. The thermoforming apparatus in accordance with claim 1,wherein said connecting rod has towards said lower tool table a Y-shapedcross-section so as to branch out into two arms and thus act on saidlower tool table via two spaced-apart locations.
 3. The thermoformingapparatus in accordance with claim 1, wherein said crankshaft drivemechanism includes an electric servomotor.
 4. The thermoformingapparatus in accordance with claim 3, wherein said electric servomotordrives said crankshaft drive mechanism through the intermediary of atoothed belt via pulleys.
 5. The thermoforming apparatus in accordancewith claim 1, wherein said lower tool table, when in a position removedfrom said upper tool table, is capable of being rotated out of saidframe of said thermoforming apparatus together with said rotatable railassembly and associated with a stacking means, so that said lower tooltable then faces said opposed stacking means, and is approached towardsand moved away from the latter.
 6. The thermoforming apparatus inaccordance with claim 2, wherein ejector drive means are arrangedbetween said two arms of said Y-shaped connecting rod which face saidlower tool table.
 7. The thermoforming apparatus in accordance withclaim 1, wherein said second drive means for generating the die-cuttingstroke include a hydraulically driven lifting cylinder.
 8. Thethermoforming apparatus in accordance with claim 1, wherein the strokeof said second drive means is about 3 mm to 10 mm.
 9. Method forproducing shaped bodies, such as cups, containers, lids, secondarypackaging for foodstuffs or the like of plastic sheet, with the aid of athermoforming apparatus for producing shaped bodies of plastic sheet,such as cups, containers, lids, secondary packaging for foodstuffs orthe like, the thermoforming apparatus comprising a forming station witha two-part forming tool, wherein the two-part forming tool comprises anupper tool table adapted to be adjustably fixed and having an upper toolwith pre-stretch means movably mounted therein, and a movable lower tooltable having a lower tool with cavities, wherein said movable lower tooltable is guided through the intermediary of guide means and capable ofbeing approached to said upper tool table and moved away from it byfirst drive means, wherein said guide means include a rotatable guiderail assembly whereby said lower tool table may be guided rectilinearlyand rotated together with said guide rail assembly, and wherein therotatable guide rail assembly includes two guide rails, pivot-mounted ona frame of the thermoforming apparatus, with the lower tool table beingguided movably between those, in a rectilinear manner, to be approachedtowards the upper tool table and moved away from the latter, comprising:the following steps: providing the thermoforming apparatus; feeding saidplastic sheet into said forming tool; tightening said plastic sheet;closing said forming tool by guiding said movable lower tool tablethrough the intermediary of said guide means and driving it through theintermediary of said drive means such that it is approached towards saidupper tool table, wherein said lower tool table is driven through theintermediary of first drive means having the form of a crankshaft drivemechanism, producing the shaped bodies in the closed condition of saidforming tool, wherein said lower tool table being lifted and loweredwith its drive means within said guide means rectilinearly guiding it,by said second drive means, in a predetermined stroke for generating adie-cutting movement, opening said forming tool by guiding said movablelower tool table through the intermediary of said guide means anddriving it through the intermediary of said first drive means such thatthe it is moved away from said upper tool table, ejecting the shapedbodies, optionally into a stacking means, wherein said lower tool tablebeing guided rectilinearly through the intermediary of a rotatable guiderail assembly for closing and opening said forming tool, and rotatedtogether with said guide rail assembly for ejecting the shaped bodies.10. The method in accordance with claim 9, wherein said lower tooltable, when in a position removed from said upper tool table, is rotatedwith said rotatable rail assembly out of said frame of saidthermoforming apparatus and associated to a stacking means, so that saidlower tool table faces said opposed stacking means then having anopposed position, and is approached towards and moved away from thelatter.
 11. The method in accordance with claim 9, wherein said lowertool table with its drive means is raised and lowered again within saidguide means rectilinearly guiding it through the intermediary of seconddrive means, for generating a die-cutting movement with a predetermineddie-cutting stroke.
 12. The method in accordance with claim 9, whereinsaid guide means include a rotatable guide rail assembly whereby saidlower tool table may be guided rectilinearly and rotated together withsaid guide assembly.
 13. The method according to claim 9, wherein saidrotatable guide rail assembly of said guide means includes two rotatableguide rails linked to a frame of said thermoforming apparatus, betweenwhich said lower tool table is guided so as to be capable of beingrectilinearly approached towards said upper tool table and moved awayfrom it.
 14. The thermoforming apparatus in accordance with claim 1,wherein the stroke of said second drive means is about 5 mm to 8 mm. 15.The thermoforming apparatus in accordance with claim 1, wherein thestroke of said second drive means is about 1.1 to 1.3 times thethickness of a plastic sheet.